1. Field of the Invention
This invention relates to magnetic resonance imaging systems. In a primary application this invention involves an MRI system that acquires a sequence of portions of the k-space of an image. Each individual portion of k-space is separately transformed and demodulated. The demodulated portions, each representing different spectral portions of the image, are summed.
2. Description of Related Art
The basic concepts in magnetic resonance are described in a series of papers in the June 1980 series of the IEEE Transactions on Nuclear Science, Vol. NS-27, pp 1220–1255. A detailed description of MRI is given in the paper by W. S. Hinshaw and A. H. Lent, “An introduction to NMR imaging: From the Bloch equation to the imaging equation”, Proceedings of the IEEE, 71(3):338–350, March 1983.
In MRI, the acquired data is the k-space or spatial Fourier transform of the image. In high-speed MRI imaging, each excitation is followed by the scan of a portion of k-space. The entire k-space is not scanned for a number of reasons. Firstly, the short imaging period would result in a poor SNR as shown in the journal paper by A. Macovski, “Noise in MRI”, Magn Reson Med 36:494–497, 1996. In addition, attempts at very rapid gradient speeds to cover all of k-space often result in exceeding the FDA dB/dt limits, causing neural stimulation. As a result, typical k-space scans involve a sequence of interleaved spirals or of sequences of parallel lines. The problem with these approaches is that motion or other changes occur between the acquisitions of these sequences. The k-space sequences are added, transformed and demodulated to provide the final image. However, as a result of the changes between sequences, significant artifacts result because of the inconsistent k-space data. Thus each sequence of k-space corresponds to a somewhat different image as a result of these changes.